Incandescent lamp system



May 1, 1934.

W. L. DAWSON INCANDESCENT LAMP SYSTEM Filed Jan. 9, 1932 INVENTOR W L.DA WSON,

Patented May 1, 1934 INCANDESCENT LAMP SYSTEM Wilfrid L. Dawson, NewYork, N. Y., assignor tc Bell Telephone Laboratories, Incorporated, NewYork, N. Y., a corporation of New York Application January 9, 1932,Serial No. 585,752

4 Claims.

This invention relates to systems for operating incandescent lamps andparticularly to' a system for operating incandescent; electric lamps onrectified alternating current.

The object of this invention is to minimize the variation in the lightemitted by an electric incandescent lamp operated on rectifiedalternating current due to the residual ripple in the rectified current.

A feature of the invention resides in the use of an electricincandescent lamp having a filament tapped at a central point.

Another feature of the invention resides in the connection of thefilament ofthe lamp in shunt with the filter of the'rectifier.

Another feature of theinvention resides in the provision of means forsupplying components of the ripple current approximately in phaseopposition to the two sections of the filament.

A further feature of the invention is the provision of a series resonantcircuit, resonant'at the fundamental frequency of the ripple current,for supplying currents in phase opposition to the sections of thefilament.

Many optical systems require a light source of very constant intensitywhich has commonly taken the form of an electric incandescent lampoperated by current from a storage battery. Because of the well knowndisadvantages of a storage battery and the wide distribution ofalternating current supplies, in recent developments, the storagebattery has been replaced by a rectifier and filter operated byalternating current. It

has been found, however, that, unless a rather elaborate filter isemployed, a varying component is superimposed on the steady currentsupplied to the lamp. When a very constant source of light is essential,the variation in the light due to this varying component may be ofsumcient magnitude to render unsatisfactory the results obtained.

In accordance with the present invention a rectifier and filter'suppliesrectified alternating current to an incandescent lamp and any otherdesired apparatus. The filament of the incandescent lamp is connected inshunt to a. section of the filter. An inductor and a capacitor in seriesare also connected in shunt to the filament of the lamp. The value ofthe inductance and capacitance is chosen so that the inductor andcapacitor form a series resonant circuit resonant at the fundamentalfrequency of the ripple component of the rectified current. The Junctionof the inductor and capacitor is connected to the midpoint of thefilament of the lamp so that the ripple currents flowing in the sectionsof the filament are approximately in phase opposition.

For certain uses, the filament of a lamp of this character must beimaged on a small area. 0 As a result, the tap in the center of thefilament must be so made that a dark spot is not caused at the tap, andequal portions of the halves of the filament may be imaged on the area.In a preferred form of lamp, a flat ribbon-like fila- 03 ment isvertically supported in the usual glass envelope. A loop at the centerof the filament is formed around a flattened leading-in wire. Aresilient, nearly circular spring retains the filament around theleading-in wire, and exerts tension on the two sections of the filamentto cause the ends-of the sections to be closely adjacent. While thisinvention is disclosed as embodied I in an incandescent lamp system, itwill be appar- 7.5- ent to one skilled in the art, that the invention isof wide application. The invention may readily be applied to any elementwhich, when heated by a periodically varying current, emits or causesthe emission of radiant energy. The invention is go thus applicable tothe ordinary thermionic vacuum tube'having a filament which, when heatedby avarying current, emits electrons. The invention is also peculiarlyapplicable to the socalled heater-type vacuum tube in which an ele- 5ment" heated by a varying current causes the emission of electrons froman indirectly-heated cathode. The invention is also applicable to heatedelements, such as the known Nernstglower, which radiate energy whenheated by a varying current, but are not necessarily enclosed in anevacuated envelope.

Fig. 1 diagrammatically represents a simplified system embodying a formof the invention.

Fig. 2 represents a sectional view of the lamp shown in Fig. 1 along theplane of the line 2-2.

Fig. 3 is a detail view of the clamp at the center of the filament ofthe lamp.

Fig. 4 diagrammatically represents a preferred form of the invention.

In Fig. 1 a foot-tube 11 is mounted in an evacuated envelope 12.Leading-in wires 13' and 14 sealed in the foot-tiibe 11 support a fiatfilament 15 in a vertical position. The leading-in wires 13 and 14 maybe arranged in the-usual way to exert a moderate spring tension on theends of the filament 15. A leading-in wire 16 sealed in the foottube 11is bent horizontally to form a center support for the filament 15. Asshown in Fig. 2, the leading-in wire 16 is bent so that the outer end isat right angles to the longitudinal axis of the filament 15. A portion1'7 of the outer end of the leading-in wire 16 is flattened in a planenormal to the plane of the filament 15, and the edge 18 of the fiattenedportion 17 may be tapered. The filament 15 is wrapped around theflattened portion 17 of the leading-in wire 16 and is retained by aresilient clamp 19.

As shown in Fig. 3, the edges of the clamp 19 in contact with thefilament 15 may be tapered to a thin edge. The clamp 19 is composed ofsome material, such as molybdenum, which does not lose its resiliencewhen heated. When the fila ment 15 is heated, the clamp 19 holds thefilament 15 taut and straight and draws the two sections of the filament15 together so that the dark area in the center of the filament ismaterially reduced.

In Fig. 1, current from a source of alternating current 20 is applied tothe primary winding of a transformer 21. A central tap on the secondarywinding of the transformer 21 is connected by wire 22 to the leading-inwire 16. An outer end of the secondary winding of transformer 21 isconnected through an inductor 23 to the leadingin wire 13. The other endof the secondary winding of transformer 21 is connected through 9.capacitor 24 to the leading-in wire 14.

The current flowing from the secondary winding of transformer 21 throughinductor 23, leading-in wire 13, lower half of filament 15, leadinginwire 16 and wire 22 may be arranged to lag behind the electromotiveforce in the secondary Winding of transformer 21 by substantially 45electrical degrees. The current flowing from the secondary winding oftransformer 21 through capacitor 24, leading-in wire 14, upper half offilament l5, leading-in wire 16, and wire 22 may be arranged to leadahead of the electromotive force in the secondary winding of transformer21 by substantially 45 electrical degrees. Thus, when one half of thefilament 15 is emitting the maximum amount of light, the other half ofthe filament is emitting the minimum amount of light. The total lightemitted by equal lengths of the filament 15 above and below theconnection with leading-in wire 16 will thus be nearly constant.

In Fig. 4 current from a source of alternating current 25 is supplied tothe primary winding of a transformer 26. Current from the secondarywinding of the transformer 26 flows through rectifier 27, inductors 28and 29 to a load 30, returning to the secondary winding of thetransformer 26 through wire 31. The load 30 may, for example, be thefilaments of a thermionic amplifier. The rectified current flowing tothe load 30 will be smoothed by the filter formed by inductors 28 and29, and thecapacitors 34 and 35, but may contain a substantial ripplecomponent.

Current from the secondary winding of the transformer 26 flows throughrectifier 27, inductor 28, leading-in wire 14, filament 15 of lamp 12,leading-in wire 13 and wire 31. The shunt path formed by the filament15of the lamp 12 will assist in reducing the ripple component in thecurrent flowing in the load 30. The ripple component remaining in thecurrent flowing in the filament 15 will, however, tend to cause thelight emitted by the lamp 12 to vary.

An inductor 32 and capacitor 33 in serial relation are connected inparallel relation to the filament 15. The inductance of the inductor 32and the capacitance of the capacitor 33 are so chosen that thecombination forms a series resonant circuit for the ripple component.The ripple component flowing in the load 30 is materially reduced bythis resonant circuit which forms a low impedance shunt for the ripplecomponent.

The junction of the inductor 32 and the capacitor 33 is joined byleading-in wire 16 to the center of the filament 15 of the lamp 12. Theripple components flowing in the two sections of the filament 15 will bein quadrature, as hereinabove described in connection with Fig. 1. Thelight emitted by the lamp 12 will thus be substantially constant due tothe reduction in the ripple component due to the resonant shunt, and theout-of-phase relation of the ripple components flowing in the twosections of the filament 15.

What is claimed is:

1. In combination, a rectifier energized by alternating current, anelectric incandescent lamp energized by the output of said rectifier, aresonant circuit comprising a capacitor and an inductor in serialrelation in shunt with the filament of said lamp said circuit beingresonant to the fundamental frequency of the unrectified component inthe output of said rectifier and a connection from the midpoint of saidfilament to the junction of said capacitor and said inductor.

2. In combination, a rectifier energized by alternating current, afilter on the output of said rectifier including inductive serieselements, capacitative shunt elements and a resonant shunt elementcomprising a capacitor and an inductor in serial relation said shuntelement being resonant to the fundamental frequency of the unrectifiedcomponent in the output of said filter, an electric incandescent lamphaving its filament in parallel relation to said resonant shunt element,and a connection from the midpoint of said filament to the junction ofsaid capacitor and said inductor.

3. In combination, a rectifier energized by periodically varyingcurrent, a radiant element heated by the output of said rectifier, aninductor and a capacitor in serial relation connected in parallelrelation with said radiant element, and

a connection from the junction of said capacitor v and said inductor toa point intermediate the

